CVE-2011-0905 in vino
Summary
by MITRE
The rfbSendFramebufferUpdate function in server/libvncserver/rfbserver.c in vino-server in Vino 2.x before 2.28.3, 2.32.x before 2.32.2, 3.0.x before 3.0.2, and 3.1.x before 3.1.1, when tight encoding is used, allows remote authenticated users to cause a denial of service (daemon crash) via crafted dimensions in a framebuffer update request that triggers an out-of-bounds read operation.
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Analysis
by VulDB Data Team • 11/07/2021
The vulnerability identified as CVE-2011-0905 represents a critical security flaw in the Vino server implementation that affects multiple versions of the VNC server software. This issue specifically targets the rfbSendFramebufferUpdate function within the server/libvncserver/rfbserver.c file, which handles the transmission of framebuffer updates to connected clients. The vulnerability manifests when the tight encoding method is employed, a compression technique designed to optimize network traffic for VNC sessions. The flaw occurs during the processing of framebuffer update requests where the server fails to properly validate the dimensions provided by authenticated remote users, creating a scenario where malicious input can trigger unexpected behavior in the software's memory management operations.
The technical exploitation of this vulnerability involves an out-of-bounds read condition that occurs when the server processes crafted framebuffer update requests containing invalid dimension parameters. This memory access violation represents a classic buffer over-read scenario that can lead to unpredictable program behavior and ultimately result in daemon crash. The vulnerability is particularly concerning because it requires only authenticated access to exploit, meaning that any user who can establish a valid VNC session can potentially trigger this denial of service condition. The flaw stems from inadequate input validation within the tight encoding processing pipeline, where dimension values are not properly sanitized or checked against acceptable ranges before being used in memory operations.
From an operational impact perspective, this vulnerability creates significant risk for VNC server deployments where multiple users may have authenticated access. The denial of service condition can result in complete disruption of VNC services, forcing administrators to restart the vino-server daemon and potentially interrupting legitimate user sessions. The vulnerability affects a broad range of Vino server versions, including the 2.x series through 3.1.x releases, indicating it was a widespread issue that likely impacted numerous deployments across different organizational environments. Security teams must consider the potential for this vulnerability to be exploited in targeted attacks where an authenticated attacker seeks to disrupt services, or in broader reconnaissance activities where the vulnerability could be used to identify vulnerable systems within a network.
The vulnerability aligns with CWE-125, which describes out-of-bounds read conditions that occur when software reads data past the boundaries of allocated buffers. This classification emphasizes the fundamental memory safety issue at the core of the problem, where the server's handling of user-supplied dimension values fails to account for proper bounds checking. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to network denial of service, as it enables an authenticated attacker to disrupt service availability. The vulnerability also connects to T1071.004 for application layer protocol, since it affects the VNC protocol implementation. Organizations should implement immediate mitigations including applying the vendor-provided patches that address the input validation issue in the rfbSendFramebufferUpdate function, and consider network-level controls that can detect and block suspicious framebuffer update patterns. Additionally, monitoring for unusual authentication patterns and service disruptions can help identify potential exploitation attempts, while maintaining up-to-date security patches remains the primary defense against this and similar memory safety vulnerabilities.